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Visual approach slope indicator (VASI)

Visual Approach Slope Indicator

Visual approach slope indicator (VASI). A visual aid of lights arranged to provide descent guidance information during the approach to the runway. A pilot on the correct glideslope will see red lights over white lights.

Basic VASI consist of two sets of lights. One set marks the start of the runway, while the other is set up some seven meters (twenty feet) behind the first. Each set of lights is designed so that the lights appear as either white or red, depending on the angle at which the lights are viewed. When the pilot is approaching the lights at the proper angle, meaning the pilot is on the glide slope, the first set of lights appears white and the second set appears red. When both sets appear white, the pilot is flying too high, and when both appear red he is flying too low. This is the most common type of visual approach slope indicator system.